In copending application U.S. Ser. No. 166,032 filed July 7, 1980, there are disclosed novel polymer compositions comprised of polyacrylonitrile polymer and block copolymer having acrylonitrile and non-crystalline polymer sequences and a process for forming such polymer compositions. Block copolymers of acrylonitrile sequences with another polymer sequences, for example, acrylamide are a two phase structure separated into domains wherein the acrylonitrile domain has a like crystalline structure to polyacrylonitrile polymer.
Such block copolymers may be readily formed by the controlled acid catalyzed hydrolysis of polyacrylonitrile polymer, and are highly swellable in water with a swelling capacity dependent on the ratio of both sequences and on the number of separate domains. Generally, the block copolymers exhibit considerable strength in the swollen state caused by the two phase structure and crystallinity of the acrylonitrile domains. The block copolymers have been shaped by pressure in the swollen state or from thermo-reversible gels (TRG), such as disclosed in U.S. Pat. No. 4,053,442 and No. 4,173,606, respectively.
With the acid catalyzed hydrolysis of polyacrylonitrile to form the acrylonitrile-acrylamide (and some acrylic acid units) block copolymers, some glutarimide units may be formed, and if formed, are small and in an amount insufficient to influence the properties of the acrylic acid - acrylamide block copolymers, i.e. hydrophilicity. The multi-block copolymers of acrylonitrile sequences with acrylamide or acrylamide and acrylic acid sequences exhibit excellent mechanical properties, but their use is limited by water swelling capabilities.
Under certain conditions, the acid catalyzed hydrolysis of polyacrylonitrile yields water insoluble copolymers (not block copolymers) of a high glutarimide content but without acrylonitrile units in crystallizable sequence. Such glutarimide containing copolymers exhibit poor mechanical properties and are, as a rule, considered to be undesirable intermediate products of a process leading to the water-soluble acrylic polymers, i.e. polyacrylic acid or the water-soluble acrylamideacrylic acid copolymers.